leakage data from British Columbia (BC) were analyzed in order to quantify the occurrence and pathways of leakage as well as the contribution to GHGemissions. The key results summarize as follows. 1) In total, 2,329 wells in BC (of 21,525 that have been tested for leakage) have had reported leakage during the lifetime of the well. 2) In total, GHGemissions are estimated to reach about 75,000 metric t/y. The study also underlines that the values of leaky wells are likely underreported. Abstract: Oil and gas well leakage is of public concern primarily due to the perceived risks of aquifer contamination and greenhouse gas (GHG) emissions. This study examined well leakage data from the British Columbia Oil and Gas Commission (BC OGC) to identify leakage pathways and initially quantify incident rates of leakage and GHGemissions from leaking wells. Three types of leakage are distinguished: 'surface casing vent flow' (SCVF), 'outside the surface casing leakage' (OSCL), and 'cap leakage' (CL). In British Columbia (BC), the majority of reported incidents involve SCVF of gases, which does not pose a risk of aquifer contamination but does contribute to GHGemissions. Reported liquid leakage of brines and hydrocarbons is rarer. OSCL and CL of gas are more serious problems due to the risk of long-term leakage from abandoned wells; some were reported to be leaking gas several decades after they were permanently abandoned. According to the requirements of provincial regulation, 21,525 have been tested for leakage. In total, 2,329 wells in BC have had reported leakage during the lifetime of the well. This represents 10.8% of all wells in the assumed test population. However, it seems likely that wells drilled and/or abandoned before 2010 have unreported leakage. In BC, the total GHGemission from gas SCVF is estimated to reach about 75,000 t/y based on the existing inventory calculation; however, this number is likely higher due to underreporting.

Wolbach, W.S., Ballard, J.P., Mayewski, P.A., Kurbatov, A., Bunch, T.E., LeCompte, M.A., Adedeji, V., Israde- Alcántara, I., Firestone, R.B., Mahaney, W.C., Melott, A.L., Moore, C.R., Napier, W.M., Howard, G.A., Tankersley, K.B., Thomas, B.C., Wittke, J.H., Johnson, J.R., Mitra, S., Kennett, J.P., Kletetschka, G., West, A., 2020. Extraordinary biomass-burning episode and impact winter triggered by the younger Dryas cosmic impact ∼ 12,800 years ago: A reply. The Journal of Geology 128, 95-107.

https://www.journals.uchicago.edu/doi/abs/10.1086/706265 New hypotheses with major multidisciplinary implications, such as the Younger Dryas airburst/impact hypothesis, appropriately face intense testing, and we respect that. However, such criticisms must be based on facts. Instead, many of the assertions made in the discussion by Holliday and coauthors are inaccurate. In this article, we present rebuttals of the most significant of their inaccurate assertions but decline to address unfounded opinions. Most of the following discussion deals with the implications of the Younger Dryas Boundary (YDB) layer, including evidence supporting extensive YDB burning and its proposed age, identification, and context within the chronological record. Other issues include the association of biomass burning with impact-related proxies, megafaunal extinctions, and human population declines. Holliday and coauthors dispute whether impacts, in general, can even cause biomass burning, a long-settled question. These issues are presented mostly in order of appearance with direct quotations from the discussion by Holliday and coauthors in boldface type within quotation marks. Emphasis has been added to some of their statements, as noted.

Reply to: Holliday, V.T., Bartlein, P.J., Scott, A.C., Marlon, J.R., 2020. Extraordinary biomass-burning episode and ∼ impact winter triggered by the Younger Dryas cosmic impact 12,800 years ago, Parts 1 and 2: A discussion. The Journal of Geology 128, 69-94.

Original Papers: Wolbach, W.S., Ballard, J.P., Mayewski, P.A., Adedeji, V., Bunch, T.E., Firestone, R.B., French, T.A., Howard, G.A., Israde-Alcántara, I., Johnson, J.R., Kimbel, D., Kinzie, C.R., Kurbatov, A., Kletetschka, G., LeCompte, M.A., Mahaney, W.C., Melott, A.L., Maiorana-Boutilier, A., Mitra, S., Moore, C.R., Napier, W.M., Parlier, J., Tankersley, K.B., Thomas, B.C., Wittke, J.H., West, A., Kennett, J.P., 2018. Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ∼ 12,800 years ago. 1. Ice cores and glaciers. The Journal of Geology 126, 165-184. Wolbach, W.S., Ballard, J.P., Mayewski, P.A., Parnell, A.C., Cahill, N., Adedeji, V., Bunch, T.E., Domínguez- Vázquez, G., Erlandson, J.M., Firestone, R.B., French, T.A., Howard, G., Israde-Alcántara, I., Johnson, J.R., Kimbel, D., Kinzie, C.R., Kurbatov, A., Kletetschka, G., LeCompte, M.A., Mahaney, W.C., Melott, A.L.,